Transcriptional and translational fusions to reporter genes whose products can be easily assayed offer powerful approaches to studying gene structure, expression, regulation, gene product assembly, transport and compartmentalization (Rosenberg et al., Science 222:734-739, 1983; Bonnerot et al., Proc. Nat. Acad. Sci. U.S.A. 84:6795-6799, 1987; Finnegan et al., The Plant Cell 1:757-764, 1989). Some of these gene fusions have been applied in more wide-ranging studies such as discerning cell lineage during development and purifying gene products (Germino et al., Proc. Nat. Acad. Sci. U.S.A. 80:6848-6852, 1983; Silhavy and Beckwith, Microbiol Rev. 49:398-418, 1985; Scholtissek and Grosse, Gene 62:55-64, 1988). Pioneered with E. coli .beta.-galactosidase (lacZ), gene fusions have been adapted to other organisms including yeast, animals and plants. While transcriptional fusions might be construed as straightforward, translational fusions require reporters which can function despite covalent addition of extraneous polypeptides to their amino- or carboxy-terminus.
Some genetic markers impart a selectable phenotype such as antibiotic resistance while other markers specify an enzymatic reporter activity for which there is a colorimetric or luminescence assay, making them suitable in combination for selection and screening. Single genetic markers which provide both of these features would be particularly useful.
The following references constitute background art:
Barnes, W. M. (1990) Proc. Natl. Acad. Sci. U.S.A. 87 9183-9187. PA0 Raju, S. S. et al. (1990) J. of Cellular Biochemistry supp. 14E: UCLA symposia on molecular and cellular biology p. 279, abstr R115. PA0 WO-A-8402913 Monsanto Company, 2 Aug., 1984 pp. 52-53. PA0 Koncz, C. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, pp. 8467-8471. PA0 Restrepo et al. 1990 The Plant Cell 2:987-998.